Several types of viruses, including retrovirus, adenovirus, adeno-associated virus (AAV), and herpes simplex virus, have been modified in the laboratory for therapeutic applications. However, each has limited applications for which it is best suited. For example, Retroviral vectors permanently integrate into the genome of the infected cell causing safety issues, and require mitotic cell division for transduction. Adenoviral vectors can deliver genes to a wide variety of dividing and nondividing cell types, but immune elimination of infected cells often limits gene expression in vivo. Herpes simplex virus can deliver large amounts of exogenous DNA; however, cytotoxicity and maintenance of transgene expression remain an obstacle. AAV infects many nondividing and dividing cell types, but has a limited DNA capacity. There plainly exists the need for a more flexible and versatile approach.